高阻GaN的MOCVD外延生长

利用金属有机化合物气相沉积(MOCVD)在蓝宝石衬底上生长了高阻GaN薄膜。对GaN成核层生长的反应室压力、生长时间和载气类型对GaN缓冲层电学特性的影响进行了分析。实验结果表明,延长GaN成核层的生长时间,降低成核层生长时的反应室压力,载气由H₂换为N₂都会得到高阻的GaN缓冲层。样品的方块电阻R_s最高为2.49×10¹¹ Ω/□。以高阻GaN样品为衬底制备了AlGaN/AlN/GaN结构HEMT器件,迁移率最高达1 230 cm²/(V·s)。     

TiN growth on Si by hybrid radical beam PLD

High-quality (good crystallinity and stoichiometry) titanium nitride (TiN) thin films were grown on Si(100) substrates by pulsed laser deposition (PLD) using a high-purity titanium target (99.99%) and nitrogen radical beam. The crystallinity, chemical composition, and depth profiles of the grown films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS), respectively. The XRD pattern indicated that the preferred growth of TiN(200) with an orientation parallel to the Si(100) direction was obtained and the nitrogen radical drastically improved crystallinity compared with that grown in ambient nitrogen gas. RBS spectra indicated that the combination of PLD and the nitrogen radical beam suppressed silicidation at the interface between the Si substrate and TiN thin film during growth. The XPS analysis revealed that this method achieved the synthesis of stoichiometric TiN films.     

Growth of AlN on clean and oxidised polycrystalline iron: an Auger study

The growth of aluminium nitride (AlN) thin films on clean and oxidised polycrystalline iron was studied by Auger electron spectroscopy. The films of AlN were deposited by reactive RF sputtering (argon + nitrogen atmosphere). On clean iron, a modelisation of the Auger peak-to-peak intensities evidences a Stranski-Krastanov growth mode (one layer followed by island formation) with an interfacial layer made of iron nitride covered by the AlN. Results on oxidised iron suggested the growth of a two-phase film with stoichiometry gradient of the (AlN)_x(Al₂O₃)_1−x form, x increasing with the film thickness. Grains of AlN in the layer were shown to favour the diffusion of oxygen from the substrate to the film until thicknesses of about 80 monolayers are reached. The presence of grains of both phases supports the hypothesis of an island growth mode for this interface.     

Crystalline silicon films sputtered on molybdenum: A study of the silicon–molybdenum interface

Polycrystalline silicon films were grown on molybdenum (Mo)-coated substrates at high deposition rate using the pulsed magnetron sputtering technique. Our study investigates the silicon–molybdenum interface of these films to elucidate stimulating mechanisms for an ordered crystalline silicon thin film growth. Both Auger electron spectroscopy and Rutherford backscattering reveal that at a substrate temperature as low as T_S=450 °C during the deposition process intermixing of Si and Mo at the Si–Mo interface takes place leading to a compositional ratio Mo:Si of about 1:2. By Raman spectroscopy hexagonal β-MoSi₂ could be identified as the dominant phase in this intermixed region. The dependence of the resulting thickness of the reacted interface layer on the deposition conditions is not fully understood yet.     

不同Sb含量p-SnO2薄膜的制备和特性

采用化学气相沉积方法, 利用Sb₂O₃/SnO作为源材料, 在蓝宝石衬底上制备出不同Sb掺杂量的SnO₂薄膜, 并在此基础上制作出p-SnO₂:Sb/n-SnO₂同质p-n 结器件. 研究表明, 随着Sb含量的增加, 样品表面变得平滑, 晶粒尺寸逐渐增大, 且晶体质量有所改善, 发现少量Sb的掺入可以起到表面活化剂的作用. Hall测量结果证实适量Sb的掺杂可以使SnO₂呈现p型导电特性, 当Sb₂O₃/SnO的质量比为1:5时, 其电学参数为最佳值. 此外, p-SnO₂:Sb/n-SnO₂同质p-n结器件展现出良好的整流特性, 其正向开启电压为3.4 V.     

Surface and interface characteristics of TiO2–muscovite nanocomposites

The morphology and chemical characteristics of the surface and the interface of TiO₂–muscovite nanocomposites were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Our results clearly showed that TiO₂ grains formed on the TiO₂ thin film surface, whereas the presence of TiO₂ grains on the interface between TiO₂ thin films and the muscovite substrates was not obvious. While euhedral rutile grains were found in samples doped with Zn ions, none were found in samples doped with Sn ions. The XPS results showed that cations present in the muscovite substrates diffused into the TiO₂ thin films. Etching measurements revealed that diffusion abilities of cation impurities varied: Si and Al diffused more easily than K. The observed differences in chemical composition and oxidation of the elements, especially on the surface and the subsurface, may influence the different crystallization behaviors of elements in TiO₂ thin films and the different active degree of elements diffusing from muscovite substrates.     

N2流量对N掺杂MgZnO薄膜结构和性能的影响

利用射频磁控溅射方法,使用Mg_{0. 04}Zn_0.96O 陶瓷靶材,选用不同流量比的氮气和氩气混和气体作为溅射气体,在石英基片上生长N掺杂Mg_xZn_1-xO合金薄膜。研究了氮流量比对薄膜组分、结构、形貌、电学性质和拉曼光谱的影响。结果显示：随着溅射气氛中氮流量比的增加,薄膜中Mg含量增加,薄膜表面颗粒尺寸减小,结晶质量变差,电阻率逐渐增大,导电类型发生转变。在氮流量比为20%时,获得了最好的p型导电薄膜。另外,随着氮流量比的增加,拉曼光谱中与N_O相关的位于272 cm^-1、642 cm^-1左右的振动峰逐渐增强,表明N_O的浓度随着氮流量比的加大而有所增加。     

Thickness dependence of microstructures in La0.9Sr0.1MnO3 thin films grown on exact-cut and miscut SrTiO3 substrates

The thickness dependence of microstructures of La_0.9Sr_0.1MnO₃ (LSMO) thin films grown on exact-cut and miscut SrTiO₃ (STO) substrates, respectively, was investigated by high-angle X-ray diffraction (HXRD), X-ray small-angle reflection (XSAR), X-ray reciprocal space mapping and atomic force microscopy (AFM). Results show that the LSMO films are in pseudocubic structure and are highly epitaxial [0 0 1]-oriented growth on the (0 0 1) STO substrates. The crystalline quality of the LSMO film is improved with thickness. The epitaxial relationship between the LSMO films and the STO substrates is [0 0 1]_LSMO[0 0 1]_EXACT-STO, and the LSMO films have a slight mosaic structure along the q_x direction for the samples grown on the exact-cut STO substrates. However, an oriented angle of about 0.24° exists between [0 0 1]_LSMO and [0 0 1]_MISCUT-STO, and the LSMO films have a mosaic structure along the q_z direction for that grown on the miscut STO substrates. The mosaic structure of both groups of the samples tends to reduce with thickness. The diffraction intensity of the (0 0 4) peaks increases with thickness of the LSMO film. The XSAR and AFM observations show that for both groups, the interface is sharp and the surface is rather smooth. The mechanism was discussed briefly.     

Superconducting Nd1.85Ce0.15CuO4 films grown by the pulsed electron deposition technique

Nd_1.85Ce_0.15CuO_4−δ superconducting thin films were prepared on (1 0 0) SrTiO₃ substrates by pulsed electron deposition technique without reducing atmosphere. Oxygen content is finely controlled by high temperature vacuum annealing, and optimal superconductivity has been obtained. The deposition conditions of the film are discussed in details. Higher deposition temperature and lower gas pressure result in the loss of copper and the appearance of the foreign phase Ce_0.5Nd_0.5O_1.75. High quality Nd_1.85Ce_0.15CuO_4−δ epitaxial films are deposited at 840–870 °C in the mixed gas with a ratio of O₂:Ar = 1:3.     

Structural, optical and electrical studies on pulse electrodeposited CdIn2S4 thin films

CdIn₂S₄ thin films were prepared by pulse electrodeposition technique over F:SnO₂ glass and stainless steel substrates in galvanostatic mode from an aqueous acidic bath containing CdSO₄, InCl₃ and Na₂S₂O₃. The growth kinetics of the film has been studied and the deposition parameters such as electrolyte bath concentration, bath temperature, time of deposition, deposition current and pH of the bath are optimized. X-ray diffraction (XRD) analysis of the as deposited and annealed films shows polycrystalline nature. Energy dispersive analysis by X-ray (EDAX) confirms nearly stoichiometric CdIn₂S₄ nature of the film. Scanning electron microscope (SEM) studies show that, the deposited films are well adherent and grains are uniformly distributed over the surface of the substrate. The optical transmission spectra show a direct band gap of 2.16 eV. Conductivity measurements have been carried out at different temperatures and electrical parameters such as activation energy, trapped energy state and barrier heights etc. have been determined.     

用激光分子束外延在Si衬底上外延生长高质量的TiN薄膜

采用激光分子束外延技术,利用两步法,在Si单晶衬底上成功地外延生长出TiN薄膜材料.原子力显微镜分析结果显示, TiN薄膜材料表面光滑,在10 μm×10 μm范围内,均方根粗糙度为0842nm.霍耳效应测量结果显示,TiN薄膜在室温条件下的电阻率为36×10^-5Ω·cm,迁移率达到5830 cm²/V·S,表明TiN薄膜材料是一种优良的电极材料.X射线θ—2θ扫描结果和很高的迁移率均表明,高质量的TiN薄膜材料被外延在Si衬底 关键词： 激光分子束外延 TiN单晶薄膜 外延生长     

Synthesis of titanium nitride thin films deposited by a new shielded arc ion plating

Thin films of titanium nitride (TiN) were deposited on stainless steel substrates by a modified deposition technique, double-layered shielded arc ion plating with vicarious circular holes (DL-SAIP). The results show that the TiN film with the distance of 10 mm between the double-layered shield plates had the least droplets. The deposition rate of the films prepared with the new technique was more homogeneous than that of all the other shielded arc ion plating. The film/substrate adhesion and microhardness values of the TiN films were higher than 40 N and 18 GPa, respectively. Thus such TiN thin films can be expected in applications.     

Growth, structural, and magnetic properties of iron nitride thin films deposited by dc magnetron sputtering

FeN thin films were deposited on glass substrates by dc magnetron sputtering at different Ar/N₂ discharges. The composition, structure and the surface morphology of the films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). Films deposited at different nitrogen pressures exhibited different structures with different nitrogen contents, and the surface roughness depended on the mechanism of the film growth. Saturation magnetization and coercivity of all films were determined using superconducting quantum interference device, which showed that if N₂/(Ar+N₂) flow ratio was equal to or larger than 30% the nonmagnetic single-phase γ″-FeN appeared. If N₂/(Ar+N₂) flow ratio was less than 10%, the films consisted of the mixed phases of FeN_0.056 and γ′-Fe₁₆N₂, whose saturation magnetizations were larger than that of -Fe. If N₂/(Ar+N₂) flow ratio was 10%, the phases of γ′-Fe₄N and -Fe₃N appeared, whose saturation magnetizations were lower than that of -Fe.     

Morphological and electrical properties of SrTiO_3/TiO_2/SrTiO_3 sandwich structures prepared by plasma sputtering

SrTiO_3(STO) and TiO_2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage(α). Insertion of a TiO_2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO_2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO_2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. Ti N was deposited as the top and bottom metal electrodes to form a metal–insulator metal(MIM) structure,which exhibited a very large linear capacitance density of 21 fF/um~2 that decreased by increasing the thickness of the TiO_2 film. The leakage current decreased with an increase in the thickness of TiO_2, and for a 27-nm-thick film, the measured leakage current was 2.0 × 10~(-10) A. X-ray diffraction and Raman spectroscopy revealed that Ti N, STO, and TiO_2 films are crystalline and TiO_2 has a dominant anatese phase structure.     

Influences of annealing on structural and compositional properties of Al_2O_3 thin films grown on 4H–SiC by atomic layer deposition

Annealing effects on structural and compositional performances of Al_2O_3 thin films on 4H–Si C substrates are studied comprehensively. The Al_2O_3 films are grown by atomic layer deposition through using trimethylaluminum and H_2 O as precursors at 300?C, and annealed at various temperatures in ambient N_2 for 1 min. The Al_2O_3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750?C to 768?C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy(XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar.     

In掺杂氮化亚铜薄膜的电学、光学和结构特性研究

采用射频磁控溅射方法, 在低功率和低温条件下利用纯氮气作为反应溅射气体制 备出不同In含量的三元氮化物Cu_xIn_yN薄膜. 研究发现In掺杂浓度对薄膜微结构、形貌、表面化学态以及光学特性有灵敏的调节作用. 光电子峰、俄歇峰、俄歇参数的化学位移变化从不同角度揭示了不同含量In掺杂引 起的原子结合情况的变化. XPS结果显示In含量小于8.2 at.%的样品形成了Cu-In-N键. 对In含量为4.6 at.%的样品进行XRD和TEM结构测试, 实验结果肯定了In原子填充到Cu₃N的反ReO₃结构的体心位置. 并且当In含量增至10.7 at.%时, 薄膜生长的择优取向从之前占主导地位的(001)方向转变为(111)方向. 此外, 随着In含量的增加, 薄膜的R-T曲线从指数形式变为线性. 当In含量为47.9 at.%时, 薄膜趋于大温区恒电阻率材料, 电阻温度系数TCR仅为-6/10000. 光谱测量结果显示In摻杂使得氮化亚铜掺杂薄膜的光学帯隙从间接帯隙变为直接帯隙. 由于Burstein-Moss效应, 帯隙发生蓝移, 从1.02 eV 到2.51 eV, 实现了帯隙连续可调. 关键词： 三元氮化物 薄膜 光学特性 氮化亚铜     

High field phenomena in thin plasma nitrided SiO2 films

The effects of high field tunnel electron injection on the electrical properties of Al - thin plasma nitrided SiO₂ films - Si (p-type) structures are studied. Under high field injection, it has been observed that electron trapping, positive charge generation near the Si-SiO₂ interface (slow states) and fast state generation at the Si-SiO₂ interface have taken place. After high temperature N₂ annealing, the nitridation induced electron trap density is considerably decreased. Furthermore, under high field injection the generation rate of both the slow states and the interface states and consequently, the degradation rate of the nitrided oxide films have been also decreased after annealing.     

Excitation, ionization, and reaction mechanism of a reactivecathodic arc deposition of TiN

This paper discusses the excitation, ionization and reaction mechanism of reactive cathodic arc deposition of TiN. Such arc plasmas art operated in the arc discharge type PVD apparatus. The 50 A arc is operated in N₂ atmosphere of 0.13 to 26.6 Pa. The arc voltage, the electron energy distribution and the spectral intensities are measured as a function of pressure. The deposited films are analyzed by XPS. It follows from the result that (1) the N₂ molecules impact with the high energy electron to be excited or ionized; (2) Ti ⁺⁺ ions which are initially emitted from the cathode spot recombine with electrons and turn Ti⁺ ions and Ti atoms and the recombination ratio increases with increasing pressure; (3) the TiN compound is produced on the substrate surface in the ensuing process, the excited N₂ are adsorbed on the substrate surface, the N ₂ are dissociated to N atoms through collisions with Ti⁺ ions of 40-60 eV, the N atoms react with the Ti atoms to form TiN     

Amorphous SiC film formation on Si(100) using electron beam excitation

The effect of electron impact on methylsilane (CH₃SiH₃) conversion to amorphous-Si_0.5C_0.5:H (a-Si_0.5C_0.5:H) films on Si(100) has been studied by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and low energy electron diffraction (LEED). It is found that electron impact greatly enhances CH₃SiH₃ decomposition on Si(100) at both 90 K and 300 K, resulting in a-Si_0.5C_0.5:H thin film formation. Thermal annealing of the film causes hydrogen desorption and amorphous silicon carbide (a-SiC) formation. Upon annealing to temperatures above 1200 K, the a-SiC film became covered by a thin silicon layer as indicated by AES studies. Ordered structures are not produced by annealing the a-SiC up to 1300 K.     

溅射气氛对N掺杂ZnO薄膜性能的影响

利用磁控溅射系统,N₂和Ar作为溅射气体,生长N掺杂ZnO薄膜。溅射气氛中氮气流量分别为0,8,20,32 mL/min,通过改变氮气的流量,研究薄膜性能的变化。结果发现,随着溅射气氛中氮气流量的增加,薄膜的电阻率增加,薄膜中N_O与(N₂)_O的掺杂浓度同时在变大。当氮气流量为8 mL/min时,N的有效掺杂效率最高。另外,随着溅射气氛中氮气流量的增加,薄膜的厚度在减小。